Referring to FIGS. 1 and 2, a conventional dipole array antenna comprises a grounded conducting substrate 12, dielectric layer 11, feeder 13 formed in a straight line along a center line of the dielectric layer 11, plurality of dipoles 14 and 15 arranged opposed with each other across the feeder 13, impedance-matching load 16 attached to one end of the feeder 13, and connector 17 attached to the other end of the feeder 13. The angle (.alpha.) formed between the feeder and dipoles 14, 15 is 45.degree.. The length (La) of the dipoles 14, 15 is one half of the center frequency (.lambda.g) of the antenna. The distance (Da) between the dipoles 14 and 15 opposed with each other across the feeder is .lambda.g/4. The distance (Db) between adjacent dipoles (Da) in any of both sides of the feeder is .lambda.g.
Since the angle (.alpha.) between the dipoles and feeder is 45.degree. and the distance (Da) between the opposed dipoles 14 and 15 is .lambda.g/4, the dipoles 14 and 15 generates a circularly polarized wave forming circles from the end of the vector representing the magnitude and direction of the electric field in the planes perpendicular to the wave transmission direction, which is combined wholly in phase in view of remote electric field. In this case, the impedance-matching load 16 attached to the one end of the feeder 13 is to prevent the incident electro-magnetic waves from being reflected from the one end of the feeder due to the impedances being not matched. However, the impedance-matching load 16 separately attached to one end of the feeder 13 and the dipoles 14 and 15 being arranged along both sides of the feeder 13 formed in a straight line increase the size of the antenna.
In order to reduce the size of the antenna, there has been proposed a circularly polarized wave array antenna disclosed in Japanese Laid-Open Patent Publication Sho 57-87603 issued on Jun. 1, 1982, wherein the dipoles and feeder are spirally formed on the same plane, so that the dipoles interfere with the feeder to cause considerable energy loss.